The present invention relates to a volumetric liquid metering device that affords an improvement over known devices for measuring volumes of liquid, particularly for use in the dairy industry. The device is also suitable for measuring fruit juice and wine, or for measuring other continuous flow liquids such as water or petroleum.
It has been found that electronic meters for the volumetric measurement of liquids, particularly milk, do not provide a sufficient degree of accuracy.
In the dairy industry it is a commonly accepted practice to allocate an amount of feed to an individual cow according to the volume of milk produced by the individual cow. For example, high volume producing cows receive more grain whilst low volume producing cows receive less grain. Accordingly, accurate measurement of the volume of milk produced per animal is required for the efficient and cost effective allocation of grain.
It is known to measure a volume of milk with a metering device comprising an electronic probe. Milk contains both butterfat and protein which behave as electrolytes. Once a certain volume of milk is accumulated in the meter, the butterfat and protein bridge an electrical circuit, thus triggering a reading. If the concentration of protein and butterfat in the milk remains constant then the accuracy of this method of volumetric measurement is satisfactory. However, in practice the concentration of butterfat and protein varies from cow to cow. Consequently, the volumetric measurement of milk with this particular device lacks consistent accuracy.
In contrast to the prior art, the present invention directly measures the volume of milk produced by the cow without relying on any other variable or parameter associated with the milk or liquid. Accordingly, the device of the present invention consistently affords a greater degree of accuracy over other prior art devices and methods.
The metering chamber of existing metering devices is calibrated in a fixed scale, for example, in liters. A further advantage of the volumetric liquid metering device of the present invention is that the operator has the option of being able to set the predetermined volume of the device and therefore is able to choose the unit of measurement in either metric or imperial units.
Today cows are producing a greater volume of milk than in the past as a result of improved genetics and better feeding techniques. Conventional methods of harvesting milk thus require increasingly larger diameter milk lines to collect the milk, which in turn need larger and more powerful vane pumps.
In current milk harvesting situations, the same line is used for the supply of vacuum to the milking plant and for the transport of milk to the milk receival vessel. The use of one line for two different purposes can be problematic, especially when a cow or a group of cows releases a surge of milk, causing the milk line to become restricted by flooding.
Flooding of the line has the effect of reducing the amount of vacuum available upstream of the restriction, often causing an interruption of vacuum supply to the upstream cows. The loss of vacuum supply upsets the cows by interrupting the milking routine and in extreme cases the upstream cow kicks off the cups.
To overcome this particular problem, the diameter of the milk line is increased to avoid interruptions to the vacuum supply. Alternatively, a system known as a loop line is installed. A loop line consists of two lines disposed parallel to one another and commonly connected at both ends to form a loop which allows the vacuum to be obtained from either side of the restriction caused by the high volume of milk.
The result of either increasing the diameter of the milk line or installing a loop line is the same. A greater demand is placed on the vane pump that supplies the vacuum. Accordingly, a large vane pump or a plurality of vane pumps is required with a consequent increase in energy consumption.
By segregating the vacuum supply from the milk transporting line there is a more uniform supply of vacuum for each cow and the milk lines do not have to be so large. It is therefore a further advantage of the present invention that when a plurality of volumetric liquid metering devices are used in a new milk harvesting situation the load on the vane pump is reduced, thus leading to energy savings.
The present invention has been designed so that it can also be installed in a dairy with conventional milk harvesting equipment such that only minor modifications to the system are required.
In accordance with one aspect of the present invention there is provided a volumetric liquid metering device comprising a meter chamber for receiving up to and including a predetermined volume of liquid, an inlet conduit for directing liquid into the meter chamber, a volumetric metering means to indicate when the predetermined volume of liquid has entered the meter chamber, and a discharge conduit for discharging liquid from the meter chamber in response to a signal from the volumetric metering means.